The present invention relates to an an electrical control system for an electrically heated window (window pane) in a motor vehicle.
For the energy supply of a heatable window of a motor vehicle, it is advantageous that the voltage is significantly higher than the normal 12 volt provided in the motor vehicle by the battery voltage. Especially in connection with the heatable front window which must be defrosted before a drive, it is necessary to provide for a short time a very high power up to 2 kilowatt. This is possible only when the voltage which is available on the heating window amounts to at least 50-60 volts.
It is possible to produce such a voltage in a very simple manner when the 3-phase voltage produced by the generator is extra decoupled and for example is high transformed through a subsequently arranged transformer. An arrangement for window heating in a motor vehicle, in which such a voltage transformation is performed by means of an auto transformer, is disclosed in the U.S. Pat. No. 4,780,619. Here the high transformed voltage is rectified by a rectifying system, the rectified voltage is used to supply a heatable window. Since the window is supplied with a high power, it must be guaranteed that it is not overheated. It is therefore provided that the temperature of the window is monitored with a temperature sensor mounted on the window, and the heating is turned off when a maxium permissible temperature is reached. This arrangement however possesses the disadvantage that a separate temperature sensor in the region of the window must be arranged, and it is connected with the voltage regulator by a relatively long conductor. This long conductor is first of all cost unfavorable, and also can be interrupted and damaged. As a result the monitoring of the window temperature cannot be guaranted in a reliable and efficient manner.